Geomorphology of an exhumed carboniferous paleosurface in the southern Gaspe Peninsula, Quebec: Paleoenvironmental and tectonic implications

Carboniferous sedimentation in the southern Gaspe Peninsula has fossilized a paleosurface which is now gradually being exhumed by erosion. Part of the surface was horizontally cut by a major peneplanation event that took plac e between 290 Ma (Permian) and 200 Ma (Jurassic). Exhumation of the surface below the peneplanation line must also have started by Jurassic time in re sponse to the en bloc uplift of the evolving Atlantic Ocean's passive margi ns. Some geomorphic features of the exhumed paleosurface bring clues regard ing Carboniferous paleoenvironments and tectonics. A planation surface limi ted by a scarp, which is leading to a higher planation surface occupied by the same rock formations, is here interpreted as a paleowave-cut platform ( associated to the Windsor transgression) for it cannot be explained by diff erential erosion, fault movement or "etchplanation". A series of fault scar ps cutting through planation surfaces are interpreted as being the result o f post-Acadian fault activity. The preservation of limestone hogbacks on th e exhumed paleosurface, which are interpreted as having evolved under an ar id climate, is believed to be either related to a pre-Windsor elastic fossi lization or to post-Windsor lateral displacement. The tightly embanked rive r system, which is still currently dissecting the Peninsula's main planatio n surface, and the karstic systems of both that surface and the exhumed pal eosurface, are interpreted as having evolved since Jurassic Time, except fo r a few cases of river antecedence in the north-central highlands which are interpreted as representing even older river routes.